Effect of image resolution and soil core diameter on soil pore characteristics quantified using X-ray computed tomography

Abstract Purpose Image resolution and size of the soil core can impact X-ray computed tomography (CT)-derived soil morphological properties. An improved understanding of soil physical properties can help elucidate contaminant transport processes through the soil profile. The main goal of this study was to compare the influence of CT scanning resolution and soil core diameter on the estimated soil pore properties. Methods Cylindrical soil cores, with diameters of 76 and 150 mm and length of 640 mm, were collected from the loamy sand soil in a cotton field located in Alabama, USA. Soil cores were collected from conventional tillage and strip tillage portions of the field, in the fall, following cotton harvest and before planting a cover crop (season 1), and in the spring, after the cover crop had matured (season 2). Specific objectives were 1) to quantify the effect of voxel resolution (0.35 mm × 0.35 mm × 0.625 vs. 0.1875 mm × 0.1875 mm × 0.625 mm) on detected soil physical properties, 2) to determine the impact of soil core diameter (150 mm vs. 76 mm) on detected soil macropore properties, and 3) to determine the effect of chosen region of interest for image analysis (140 mm vs. 96 mm diameter region of interest) on estimated soil pore properties. Results and Discussion Results on change in derived soil pore properties as a function of soil core diameter and resolution show that a smaller field of view, which gave higher resolution, showed a greater number of isolated pores with greater values of anisotropy. The 76 mm soil core diameter had significantly fewer detected pores compared to 150 mm diameter cores, but the connectivity of pores was greater for the 76 mm diameter cores. Most of the significant differences were found among the cores, which were collected from the conventional tillage treatment in season 2. Conclusions Image resolution and sample size impacted the estimated properties of the soil pores. Finer resolution achieved using a smaller field of view showed a greater number of isolated pores with greater values of anisotropy. For a similar field of view, the larger diameter core had greater pore number density and surface area density as compared to the smaller diameter core. Future research should employ high-resolution X-ray CT scanners to quantify the impact of resolution on derived soil pore properties.